Mass Loss from Red Giant Branch (and AGB) Stars in Globular Clusters Andrea Dupree Harvard-Smithsonian Center for Astrophysics AGB Workshop: 20 May 2010

Stellar Evolution  Outline is solid  Important aspects unresolved: mass loss, Second parameter….  Globular clusters a classical testing ground to confront these issues

Problems remain  Mass loss necessary for evolution, but not detected directly  Mass lost not found in globular clusters  Metallicity [Fe/H] creates differences (‘first parameter’), but…something else is at work…(‘second parameter’) Candidates for 2 nd parameter: total cluster mass; age; environment; free-floating planets; primordial He abundance; post-mixing surface He abundance; CNO abundance; stellar rotation; mass loss; more than one… Here focus on mass loss from the cool stars …

How to detect mass loss Cool stars with 2 relevant attributes (based on the Sun, mostly) 1.Chromosphere and coronas T >T photosphere 2. Dynamics controlled by magnetic field configuration: not spherically symmetric. 3. Dust (historic mass loss) Thus, need to choose diagnostics wisely, and expect variability Yohkoh x-ray image of Sun Model of metal-poor giant

Hectochelle at MMT Meszaros, S. et al. 2008, 2009, AJ Fibre (240)-fed echelle (A. Szentgyorgyi & D. Fabricant) R~34,000; 1 degree FOV Outstanding for cluster studies

Dynamics from H-α Wing emission present in luminous stars Asymmetry varies But H-alpha core shift/asymmetry always indicates outflow (or static) Suggests pulsation in lower layers creates steady outflow at top of chromosphere Meszaros et al. 2009, AJ Red giants in M92

Dynamics from H-α H-α core shift largest for luminous stars Velocities 0-~15 km s -1 ; variability in AGB stars Outflow speeds may distinguish AGB from RGB Meszaros et al Meszaros et al Flows are outflows; not escape speeds signaling a wind.

Higher up… Ca II K Ca K 3 ( ● ) indicates higher outflow velocity than H-α (×) Meszaros et al. 2009, AJ K3K3 Magellan spectra of Omega Cen giants

So, what about the mass loss rate? Only reliable way for M_dot from H-α uses non-LTE spherical models with mass flow Semi-empirical models of the atmospheres constructed for ~20 globular cluster red giants (M15, M92, M13) to match profiles Meszaros et al 2009

Current ‘laws’ overestimate mass loss Mass loss increases with L and with decreasing T EFF Suggestion of metallicity dependence Rates are ~order magnitude less than ‘Reimers’ and IR results Meszaros et al 2009 ‘Dust’ rate (to be corrected; Boyer et al. 2010) “Reimer’s rate”

AGB Stars with ‘dust’ Filled squares mark dusty AGB stars id’d by Spitzer (Boyer et al. 2006) H-α bisector velocity similar to stars with no dust. H-α mass loss rate similar to stars with no dust. K479 K421 K479 K421

K825 in M15 (RGB/AGB at tip) Direct evidence for pulsation McDonald, I. et al. 2010, MNRAS ΔT [K] ΔL [solar luminosities] NO dust in K825: pulsations do not lead to dust production Pulsation period: ~350 days; LPV; [Fe/H]=-2.5 SED validates change in T and Luminosity Accelerating outflows

Abundances returned to the ism… A lesson from the Sun… The helium abundance found in the solar wind varies depending on solar activity and wind speed…. (Kasper et al. 2007) YEAR HELIUM ABUNDANCE

Conclusions  Developing a consistent picture of mass loss in metal poor stars  H-alpha, Ca K give evidence for accelerating fast outflows from the majority of metal-poor field RGB and AGB stars  AGB objects show faster outflows and more variability than RGB stars  No difference in dynamics between ‘dusty’ stars and stars with no IR excess  Pulsation can drive outflow without dust  Inferred mass loss provides confirmation needed for stellar evolution calculations